1. Field of the Invention
The present invention relates to a flat antenna unit for a mobile communication equipment and more particularly to a technology which can enhance a communication sensitivity of a portable telephone by pasting the antenna unit on the back thereof.
2. Description of Related Art
When a mobile radio communication equipment such as a portable phone is used at places where the strength of electric field is low like a valley between tall buildings, within a building and within a vehicle, its radio efficiency drops, thus causing troubles in communication such as noise and speech interruption.
Then, in order to eliminate such troubles, there have been provided various antenna units including a so-called seal type flat antenna which is pasted on the back of a portable phone.
For instance, Japanese Utility Model Publication No. 3015919 has disclosed a flat antenna unit in which two antenna sect ions having symmetrical shapes and in which tuning capacitors are formed at both ends thereof are connected via a coupling circuit and both ends of the coupling circuit are connected by a feeder line. Further, Japanese Patent Laid-Open No. Hei. 5-259724 has disclosed a printed antenna similarly provided with feeding points and grounding sections.
Japanese Patent Laid-Open No. Hei. 6-140822 has disclosed a flat antenna unit in which a layer of a conductive material is provided on a supporting member and a receiving circuit is provided thereon as a receiving element of the flat antenna unit.
Still more, Japanese Patent Laid-open No. Hei. 4-14304 has disclosed a bi-directional loop antenna in which a conductor of a reactance element is added to each loop conductor so as to bring antenna impedance closer to terminal resistance.
By the way, the flat antenna unit must be miniaturized, lightened and thinned in order to paste on the back of the portable phone and is required that an occupied area of its antenna pattern is small, the rate of dielectric loss is low, the radio efficiency is high, the sensitivity is high, and the like.
From these points of view, the flat antenna unit disclosed in Japanese Utility Model Publication No. 3015919 has had a problem that the two symmetrical antenna sections in which the tuning capacitors are formed at the both ends must be connected by the coupling circuit and the impedance of the coupling circuit must be adjusted with the impedance of the antenna sections so that they are equalized. Similarly to that, the flat antenna unit disclosed in Japanese Patent Laid-Open No. Hei. 5-259724 has had a problem that it requires the feeding points and the grounding points, thus increasing the occupied area of the antenna pattern. The flat antenna unit disclosed in Japanese Patent Laid-Open No. Hei. 6-140822 has had problems that not only the layer of the conductive material must be provided on the supporting member but also the receiving circuit must be provided thereon in the receiving element of the flat antenna unit and that the process for forming the receiving circuit is complicated because it is formed by means of hot resist technology. The bi-directional loop antenna disclosed in Japanese Patent Laid-Open No. Hei. 4-14304 has had a similar problem that the process for forming the circuit is complicated because the occupied area of the relatively simplified antenna pattern is reduced by bringing the antenna impedance closer to the terminal resistance.